We had a power outage like that a couple of years ago, we had no power for almost 24 hours. I gathered up all of my hand and toe warmers I had laying around for skiing and heat packs for shipping fish, activated them and wrapped them around my fish tanks with towels to keep them insulated. The hand and toe warmers only last about 12 hours, but most power outages don't last that long. For the most part, it kept my fish tanks nice and toasty! I am sure you could do the same for hermies. Since then, I always try to keep some extra hand and toe warmers and heat packs on hand, just in case.
